1. Field of the Invention
In at least one aspect, the present invention provides an improved support for a catalyst placed within an exhaust system.
2. Background Art
Virtually every modern automobile contains an exhaust system for removing various environmentally harmful byproducts of an internal combustion engine. Also, many combustion furnaces, and electrical generators use catalytic convertors. Typically, various catalysts are used to accomplish this removal. These catalysts are exposed to a wide range of temperatures from below freezing up to several hundred degrees Fahrenheit. An important requirement in the design of exhaust systems is the mounting of a support of the catalyst. The material selection for these support systems must securely hold the catalyst in place at all temperatures to which the catalyst is exposed.
Several methods exist for supporting exhaust catalysts in an exhaust system. For example, knitted wire mesh supports or mat supports have been used to securely hold exhaust catalysts in place. The knitted wire mesh support has a lower maximum use temperature and a lower thermal insulating value. Moreover, knitted wire mesh supports tend to be expensive. Therefore, it is only used for applications where the temperature is so low and the use of mat is precluded.
Mat supports are ideal from many standpoints except cold holding ability. Such mat supports often contain a vermiculite popping filler that requires >500° F. for an extended time to expand the filler and cause a compressive force on the substrate. Mat supports without filler (non-intumescent type) also exist, but these supports are more expensive and harder to process to a minimum substrate holding pressure.
In another variation, an exhaust catalyst is supported by a fiber mat interwoven into a knitted wire mesh. This design is used to improve the thermal insulating value (i.e. reduce shell temperatures for heat management). However, this design is even more expensive than knitted wire mesh supports. In another prior art design, a corrugated metal inner liner is inserted into a pocket cut into a mat support. The corrugated metal is not on the outer part of the support, but on the inside. Its function is to prevent abrasion of the ceramic fiber mat in a space between two non-butted substrates and provide support for the catalyst. The purpose of the corrugation is to prevent sagging of the metal at high temperatures. However, the use of this last design is somewhat undesirable for catalyst support systems because the sandwiching of the corrugated metal greatly reduces its resiliency.
Accordingly, there exists a need in the prior art for improved catalyst supports that have a wider useful temperature range.